Evaporative body-fluid containers and methods

ABSTRACT

Body-fluid containers, methods, and systems are presented that include a container that has a container housing formed, at least in part, by a liquid-impermeable, vapor-permeable material. The liquid-impermeable, vapor-permeable material allows water to evaporate and be transmitted outside of the container. The evaporation allows more fluid to be processed by the container than the container could otherwise hold. Other systems, methods, and apparatuses are presented.

RELATED APPLICATION

The present invention is a continuation of U.S. patent application Ser.No. 14/315,136, entitled “Evaporative Body-Fluid Containers andMethods,” filed 25 Jun. 2014, which is a continuation application ofU.S. patent application Ser. No. 13/084,758, entitled “EvaporativeBody-Fluid Containers and Methods,” filed 12 Apr. 2011, now U.S. Pat.No. 8,821,458, which claims the benefit, under 35 USC § 119(e), of thefiling of U.S. Provisional Patent Application Ser. No. 61/359,181,entitled “Dressings and Methods For Treating a Tissue Site On APatient,” filed 28 Jun. 2010, which claims priority from U.S.Provisional Patent Application Ser. No. 61/359,205, entitled“Evaporative Body Fluid Containers and Methods,” filed 28 Jun. 2010,which claims priority from U.S. Provisional Patent Application Ser. No.61/325,115, entitled “Reduced-Pressure Sources, Systems, and MethodsEmploying A Polymeric, Porous, Hydrophobic Material,” filed 16 Apr.2010, each of which is incorporated herein by reference for allpurposes.

BACKGROUND

The present disclosure relates generally to medical treatment systemsand, more particularly, but not by way of limitation, to evaporativebody fluid containers, systems, dressings, and methods. The evaporativebody fluid containers, systems, dressings, and methods may be used withreduced-pressure treatment systems.

Clinical studies and practice have shown that providing a reducedpressure in proximity to a tissue site augments and accelerates thegrowth of new tissue at the tissue site. The applications of thisphenomenon are numerous, but application of reduced pressure has beenparticularly successful in treating wounds. This treatment (frequentlyreferred to in the medical community as “negative pressure woundtherapy,” “reduced pressure therapy,” or “vacuum therapy”) provides anumber of benefits, which may include faster healing and increasedformulation of granulation tissue. Typically, reduced pressure isapplied to tissue through a porous pad or other manifold device. Theporous pad contains cells or pores that are capable of distributingreduced pressure to the tissue and channeling fluids that are drawn fromthe tissue. As the reduced pressure is applied, body fluids, e.g.,exudates, are received and typically contained in a reservoir.

SUMMARY

According to one illustrative embodiment, a system for treating a tissuesite on a patient includes a treatment manifold for placing proximate tothe tissue site, and a sealing member for forming a fluid seal over thetreatment manifold and a portion of the patient's epidermis. The sealingmember is for forming a sealed treatment space over the tissue site,wherein the sealed treatment space receives fluids. The system furtherincludes a reduced-pressure source for providing reduced pressure and acontainer fluidly coupled to the reduced-pressure source and to thesealed treatment space for receiving fluids. The container includes acontainer housing having an interior space for receiving the fluids anda fluid inlet through the container housing. The fluid inlet is forreceiving the fluids into the interior space of the container housing.At least a portion of the container housing includes aliquid-impermeable, vapor-permeable material that allows egress ofevaporated liquids from the fluids.

According to another illustrative embodiment, a container for receivingand processing body fluids (primarily liquids) includes a containerhousing having an interior space for receiving the body fluids and abody fluid inlet through the container housing. The body fluid inlet isfor receiving body fluids into the interior space of the containerhousing. At least a portion of the container housing comprises aliquid-impermeable, vapor-permeable material.

According to another illustrative embodiment, a method for removing andprocessing body fluids from a patient includes removing the body fluidsfrom the patient and causing the body fluids to enter into a container.The container includes container housing having an interior space forreceiving the body fluids and a body fluid inlet through the containerhousing. The body fluid inlet is for receiving body fluids into theinterior space of the container housing. At least a portion of thecontainer housing includes a liquid-impermeable, vapor-permeablematerial. The method further includes evaporating and removing at leasta portion of the body fluids using the liquid-impermeable,vapor-permeable material.

According to another illustrative embodiment, a wound dressing fortreating a wound on a patient includes an absorbent layer having a firstside and a second, patient-facing side. The absorbent layer is in fluidcommunication with the wound. The wound dressing also includes aliquid-impermeable, vapor-permeable layer covering the absorbent layerand the wound. The liquid-impermeable, gas-impermeable layer is operableto allow body fluids from the absorbent layer to evaporate and exit theliquid-impermeable, gas-impermeable layer.

According to another illustrative embodiment, a method of manufacturinga container for receiving body fluids includes forming a containerhousing having an interior space for receiving the body fluids andforming a body fluid inlet on the container housing. The body fluidinlet is for receiving body fluids into the interior space of thecontainer housing. At least a portion of the container housing includesa liquid-impermeable, vapor-permeable material that allows evaporatedbody fluids (vapor) to egress the interior space.

Other features and advantages of the illustrative embodiments willbecome apparent with reference to the drawings and detailed descriptionthat follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, perspective view of an illustrative, non-limitingmedical treatment system that includes an illustrative embodiment of acontainer for receiving and processing body fluids;

FIG. 2 is a schematic cross section of the illustrative container forreceiving and processing body fluids of FIG. 1;

FIG. 3 is a schematic, perspective view, with a portion exploded, of anillustrative embodiment of a container for receiving and processing bodyfluids;

FIG. 4 is a schematic cross section of a portion of the container ofFIG. 3 during operation;

FIG. 5 is a schematic, front elevational view of an illustrativeembodiment of a container for receiving and processing body fluids;

FIG. 6 is a schematic cross section of the container of FIG. 5;

FIG. 7 is a schematic cross section of an illustrative embodiment of acontainer for receiving and processing body fluids;

FIG. 8 is schematic perspective view of an illustrative embodiment of acontainer for receiving and processing body fluids;

FIG. 9 is a schematic cross section of an illustrative embodiment of awound dressing for treating a wound on a patient;

FIG. 10 is a schematic cross section of an illustrative embodiment of acontainer for receiving and processing body fluids;

FIG. 11 is a schematic cross section of an illustrative embodiment of acontainer for receiving and processing body fluids;

FIG. 12 is a schematic cross section of a portion of aliquid-impermeable, vapor-permeable material for use with a container ordressing for receiving and processing body fluids;

FIG. 13 is a schematic cross section of a portion of aliquid-impermeable, vapor-permeable material for use with a container ordressing for receiving and processing body fluids;

FIG. 14 is a schematic cross section of a portion of aliquid-impermeable, vapor-permeable material for use with a container ordressing for receiving and processing body fluids;

FIG. 15 is a schematic cross section of an illustrative embodiment of acontainer for receiving and processing body fluids;

FIG. 16 is a schematic cross section of an illustrative embodiment of acontainer for receiving and processing body fluids; and

FIG. 17 is a schematic cross section of an illustrative embodiment of acontainer for receiving and processing body fluids.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings that form a part hereof.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the inventions, and it is understood thatother embodiments may be utilized and that logical structural,mechanical, electrical, and chemical changes may be made withoutdeparting from the spirit or scope of the inventions. To avoid detailnot necessary to enable those skilled in the art to practice theembodiments described herein, the description may omit certaininformation known to those skilled in the art. The following detaileddescription is not to be taken in a limiting sense, and the scope of theillustrative embodiments is defined only by the appended claims.

Referring to the drawings and primarily to FIGS. 1-2, an illustrativeembodiment of a medical treatment system 100, such as a reduced-pressuretreatment system 102, is presented. The reduced-pressure treatmentsystem 102 includes an illustrative embodiment of a container 104 forreceiving and processing body fluids (primarily liquids) from a patient103. The container 104 is operable to process more liquids over timethan the container 104 can physically retain at one time.

The reduced-pressure treatment system 102 may include a treatmentmanifold 105 that is placed proximate to a tissue site 106, such as awound 108. The wound 108 is shown through the patient's epidermis 110.The tissue site 106 may be the bodily tissue of any human, animal, orother organism, including bone tissue, adipose tissue, muscle tissue,dermal tissue, vascular tissue, connective tissue, cartilage, tendons,ligaments, or any other tissue.

The treatment manifold 105 and a portion of the patient's epidermis 110may be covered by a sealing member 112 to form a sealed treatment space116. The sealing member 112 may be any material that provides a fluidseal. The sealing member 112 maybe, for example, an impermeable orsemi-permeable, elastomeric material. “Elastomeric” means having theproperties of an elastomer. Elastomeric generally refers to a polymericmaterial that has rubber-like properties. More specifically, mostelastomers have ultimate elongations greater than 100% and a significantamount of resilience. The resilience of a material refers to thematerial's ability to recover from an elastic deformation. Examples ofelastomers may include, but are not limited to, natural rubbers,polyisoprene, styrene butadiene rubber, chloroprene rubber,polybutadiene, nitrile rubber, butyl rubber, ethylene propylene rubber,ethylene propylene diene monomer, chlorosulfonated polyethylene,polysulfide rubber, polyurethane (PU), EVA film, co-polyester, andsilicones. Additional specific examples of sealing members 112 include asilicone drape, 3M Tegaderm® drape, PU drape, such as one available fromAvery Dennison Corporation of Pasadena, Calif.

An attachment device 114 may be used with the sealing member 112 to forma fluid seal over the wound 108 and the treatment manifold 105. Theattachment device 114 may take numerous forms. For example, theattachment device 114 may be a medically acceptable, pressure-sensitiveadhesive or a hydrocolloid material that extends about a periphery ofthe sealing member 112. The sealing member 112 forms the sealedtreatment space 116 in which the treatment manifold 105 is disposed.Reduced pressure is supplied to the sealed treatment space 116, and bodyfluids 130 are thereby removed from the sealed treatment space 116.

A reduced-pressure interface 118 may be used to fluidly couple a firstreduced-pressure delivery conduit 120 to the sealed treatment space 116.In one illustrative embodiment, the reduced-pressure interface 118 is aT.R.A.C.® Pad or Sensa T.R.A.C.® Pad available from KCI of San Antonio,Tex. Other devices may be used for the reduced-pressure interface 118provided that the reduced pressure is delivered to the sealed treatmentspace 116.

The first reduced-pressure delivery conduit 120 is fluidly coupled tothe container 104 and delivers the body fluids 130 to the container 104.The container 104 receives reduced pressure from a reduced-pressuresource 122 via a second reduced-pressure delivery conduit 124. Thereduced-pressure source 122 may be any device for supplying a reducedpressure, such as a vacuum pump, wall suction, or other source. Whilethe amount and nature of reduced pressure applied to a tissue site willtypically vary according to the application, the reduced pressure willtypically be between −5 mm Hg (−667 Pa) and −500 mm Hg (−66.7 kPa) andmore typically between −75 mm Hg (−9.9 kPa) and −300 mm Hg (−39.9 kPa).For example, and not by way of limitation, the pressure may be −12,−12.5, −13, −14, −14.5, −15, −15.5, −16, −16.5, −17, −17.5, −18, −18.5,−19, −19.5, −20, −20.5, −21, −21.5, −22, −22.5, −23, −23.5, −24, −24.5,−25, −25.5, −26, −26.5 kPa or another pressure.

The container 104 receives the body fluids 130. The body fluids 130 areremoved from the body by the reduced-pressure treatment system 102. Forexample, exudates, ascites, or other body fluids are usually removed andplaced in the container 104. Many body fluids, e.g., exudates, aresubstantially water based. The exudates in a fluid reservoir, without anadditive, will not typically change state to a solid or gel, but in thepresent embodiment may change to a gel state as water is removed througha liquid-impermeable, vapor-permeable material 136.

The container 104 may be rigid, semi-rigid, or flexible. The container104 includes a container housing 126 having an interior space 128 forreceiving the body fluids 130. The container housing 126 has a bodyfluid inlet 132 for receiving the body fluids 130 and a reduced pressureinlet 134 for receiving reduced pressure. In some embodiments thatinclude a multi-lumen conduit (a lumen for reduced pressure supply andone for body fluids), the reduced-pressure inlet 134 may be the same asthe body fluid inlet 132. At least a portion of the container housing126 is formed from the liquid-impermeable, vapor-permeable material 136.In the illustrative embodiment of FIGS. 1-2, the portion of thecontainer housing 126 with the liquid-impermeable, vapor-permeablematerial 136 is a window 138, but numerous locations are possible. Thewindow 138 may be formed by forming at least one window aperture 135 andcovering the window-aperture with the liquid-impermeable,vapor-permeable material 136. The container housing 126 may be formedwith any stiffness, e.g., rigid, flexible, semi-rigid, etc.

The liquid-impermeable, vapor-permeable material 136 may form the wholecontainer 104, or fluid reservoir, or may form only a portion, e.g., awall or window 138. Typically, a higher evaporation can be obtained byhaving liquids within the container 104 in direct contact with theliquid-impermeable, vapor-permeable material 136.

In addition to having the liquid contact the liquid-impermeable,vapor-permeable material 136, a higher evaporation rate may be achievedby adding thermal energy to the body fluids 130, increasing air flowacross the exterior of the liquid-impermeable, vapor-permeable material136 (see FIGS. 10-11), or otherwise adding energy to the body fluids orair inside the container. The thermal energy may be added by deliveringthermal energy from a vacuum pump for the reduced-pressure treatmentsystem to the body fluids 130. For example, as shown in FIG. 6, if apiezoelectric pump 354 is used, the piezoelectric pump 354 may bedisposed in a container 304 so that any heat developed by thepiezoelectric pump 354 is delivered to the body fluids 330 therein. Inanother illustrative embodiment, a dedicated heating element (notshown), e.g., a resistor element, may be added to the interior space 128of the container 104. In still another illustrative embodiment, anagitator (not shown) may be added to move the body fluids 130 againstthe liquid-impermeable, vapor-permeable material 136 to facilitateevaporation and transmission. In another illustrative embodiment, theair flow on an exterior of the liquid-impermeable, vapor-permeablematerial 136 may be increased, such as by a fan or other ventilationsubsystem, to increase the evaporation rate. In another illustrativeembodiment, the container 104 is placed adjacent to the patient'sepidermis 110 to use thermal energy from the patient 103 to promoteenhanced evaporation. In another illustrative embodiment, a chemical maybe added to the interior space 128 to cause an exothermic reaction whenmixed with exudates.

The liquid-impermeable, vapor-permeable material 136 material allowswater vapor to exit or egress as suggested by arrows 140 (FIG. 2) whileretaining liquids. At the same time, the liquid-impermeable,vapor-permeable material 136 allows a reduced pressure to be maintainedwithin the container 104. The liquid-impermeable, vapor-permeablematerial 136 comprises any material that is capable of preventingliquids from ingress or egress through the material and yet is operableto permit vapor, e.g., evaporated water from the body fluids, to egressor to be transmitted through the material. Non-limiting, illustrativeexamples of the liquid-impermeable, vapor-permeable material 136 includea high moisture vapor transmission rate (MVTR) films or other structuresformed from hydrophilic polymers. Illustrative materials may includepolyvinyl alcohol, polyvinyl acetate, cellulose based materials (ethers,esters, nitrates, etc.), polyvinyl pyrrolidone, polyurethanes,polyamides, polyesters, polyacrylates and polymethacrylates,polyacrylamides. The materials for the liquid-impermeable,vapor-permeable material 136 may be crosslinked, blended, grafted, orcopolymerized with each other.

In some embodiments, the materials for forming the liquid-impermeable,vapor permeable material may be surface treated to enhancehydrophylicity. The surface treatments may include chemical, plasma,light (UV), corona, or other ionizing radiation. In some embodiments,the material for forming the liquid-impermeable, vapor permeablematerial may be formed by forming (casting) films and crosslinking someof the natural gums, such as guar, xanthan and alginates, or gelatin.The materials used for the liquid-impermeable, vapor permeable materialtypically also serve as a bacteria barrier. While the material forforming the liquid-impermeable, vapor permeable materials herein isfairly impervious to nitrogen and oxygen, the material is pervious towater vapor. One specific, non-limiting example of a suitable materialis a 15 micron sheet of Hytrel APA60015 from E. I. du Pont de Nemoursand Company of Wilmington, Del., U.S.A.

Practical issues, e.g., odor and condensation, related to the container104 may be addressed in a number of ways. First, with respect to anypotential odor, a charcoal filter or a silver impregnated mesh may beused as part of the fluid path, e.g., in the first reduced-pressuredelivery conduit 120 or body fluid inlet 132, to kill bacteria and toaddress the aroma of the vapor exiting the container 104. The risk ofcondensate on the container 104 may be reduced by managing theevaporation rate and by the design of the container 104 to ensure thatthere are no mechanical surfaces adjoining the evaporation surface thatcan be at a different temperature than the body fluids 130.

According to one illustrative embodiment, in operation, the treatmentmanifold 105 is disposed proximate to the tissue site 106. The sealingmember 112 is placed over the treatment manifold 105 and a portion ofthe patient's epidermis 110 to form the sealed treatment space 116. Ifnot already installed, the reduced-pressure interface 118 is installedon the sealing member 112 and the first reduced-pressure deliveryconduit 120 is fluidly coupled to the reduced-pressure interface 118 andthe body-fluid inlet 132 of the container 104. The secondreduced-pressure delivery conduit 124 is fluidly coupled to thecontainer 104 and the reduced-pressure source 122.

The reduced-pressure source 122 is activated. Reduced pressure isdelivered to the tissue site 106 and the body fluids 130 are removedfrom the tissue site 106. The body fluids 130 are delivered through thebody-fluid inlet 132 into the interior space 128 of the container 104.The water content of the body fluids 130 evaporates, at least in part,over an elapsed time period and is transmitted through theliquid-impermeable, vapor-permeable material 136.

As the liquids—typically water—in the body fluids 130 evaporate, adesiccated slurry results in the container 104 that contains non-waterbased products and other substances, such as proteins, fats, or salts(e.g., sodium, calcium, and chloride). The desiccated slurry willtypically congeal and change state to be a solid or gel. Thus, thedesiccated slurry may gel without an isolyzer. In some embodiments, anisolyzer may be added nonetheless.

Varying degrees of water may evaporate from the body fluids 130depending on, among other things, the time allowed, temperature, andpressure. In some instances, greater than 5% of the water in thecontainer 104 may evaporate. In other instances, greater than 10%, 20%,30%, 40%, 50%, 60%, 70%, 80%, 90% or even more of the water in thecontainer 104 may evaporate. The implicit ranges include all numbers inbetween.

The embodiment of the container 104 allows a smaller fluid reservoirbecause the container 104 is capable of processing more fluid volume(V_(f)) than the physical volume (V_(c)) of the container 104, i.e.,operatively V_(f)>V_(c). In some embodiments, the followingrelationships hold: V_(f)>105% V_(c); V_(f)>110% V_(c); V_(f)>120%V_(c); V_(f)>130% V_(c); V_(f)>150% V_(c); or V_(f)>200% V_(c). Otherratios are possible. As one illustrative, non-limiting example, thecontainer 104 may hold 500 ml (V_(c)=500 ml), but over three days of usemay receive 600-1000 ml of fluid (V_(f)=600 to 1000 ml). The smallersize reduces the cost of the container 104 for the reduced-pressuretreatment system 102 or other system requiring body fluid collection.Because a smaller container may be used with a given medical treatmentsystem, less polymer use is necessary and the cost of thereduced-pressure treatment system 102 may be reduced. The smallercontainer 104 is also typically more convenient for the patient. If thesame size container is used, it will need changing less frequently thanit otherwise would. The less frequent changes present a cost savingswith respect to the patient's care.

The evaporative process within the container 104 may produce a reducedpressure itself. Thus, when the container 104 is used as part of areduced-pressure treatment system 102, the resultant reduced pressurefrom the evaporative process augments the reduced pressure supplied bythe reduced-pressure source 122 or potentially may make redundant thereduced-pressure source 122. In addition, in the present, illustrativeembodiment, the body fluids 130 received into the container 104 mayincrease in density sufficiently to not require an isolyzer.Alternatively, a relatively reduced amount of isolyzer may be used.

Referring now primarily to FIGS. 3 and 4, another illustrativeembodiment of a container 204 for receiving and processing body fluids230 is presented. The container 204 may be used as part of a medicaltreatment system, such as the system 100 of FIG. 1. The container 204includes a container housing 226 having an interior space 228 forreceiving the body fluids 230. The container housing 226 may be formedfrom a container frame 242 and a plurality of baffles 244. The baffles244 help form a plurality of waffle pockets 246, which are smallcompartments that are interconnected by apertures (not shown) in thebaffles 244. (In another embodiment, the waffle pockets may be fluidlycoupled by a common area, such as an open space above (for orientationwith gravity) the waffle pockets). A liquid-impermeable, vapor-permeablematerial 236 is coupled to the container frame 242, such as by a weld250 on a flange portion 248 of the frame member, or container frame 242.The liquid-impermeable, vapor-permeable material 236 may also be coupledto the ends of baffles 244 between the waffle pockets 246 in someembodiments. The baffles 244 may be uniform as shown or be at differentdimensions to create more surface area for the liquid-impermeable,vapor-permeable material 236.

A body fluid inlet 232 may be formed on the container housing 226. Thebody fluid inlet 232 is for receiving the body fluids 230 into theinterior space 228 of the container housing 226. A reduced pressureinlet 234 may also be formed in the container housing 226 to allowreduced pressure into the interior space 228. In another illustrativeembodiment, reduced pressure may be omitted and the body fluidsdelivered with positive pressure. In such an embodiment, a vent opening(not shown) may be added.

As shown in FIG. 4, the waffle pockets 246 help increase the surfacearea of the liquid-impermeable, vapor-permeable material 236 that thebody fluids 230 contacts. The increased surface area may enhanceevaporation and vapor transmission of liquids from the body fluids 230.The vapor exiting the container 204 is suggested by arrows 240.

Referring now primarily to FIGS. 5-6, another illustrative embodiment ofthe container 304 for receiving and processing body fluids 330 ispresented. The container 304 may be used as part of a medical treatmentsystem, such as the system 100 of FIG. 1. The container 304 includes acontainer housing 326 having an interior space 328 for receiving thebody fluids 330.

The container housing 326 has a housing 350 formed from a firstmaterial, such as rigid polymer, and formed with a plurality ofapertures 352. The apertures 352 may take any shape, e.g., elongatedslits, squares, triangles, but are shown as annular openings. Aliquid-impermeable, vapor-permeable material 336 may be coupled to aninterior portion of the housing 350 over the plurality of apertures 352.Alternatively, the liquid impermeable, vapor-permeable material 336 maybe coupled to an exterior portion of the housing 350 over the pluralityof apertures 352. A wicking member 337 is associated with theliquid-impermeable, vapor-permeable material 336 to enhance the transferrate. The wicking member 337 may be coupled to or disposed proximate tothe liquid-impermeable, vapor-permeable material 336. Theliquid-impermeable, vapor-permeable material 336 may be welded, bonded,or coupled using any technique or device.

A plurality of windows 338 are formed having the liquid-impermeable,vapor-permeable material 336 separating the interior space 328 and anexterior. The windows 338 may be formed by forming a plurality of windowapertures 335 and covering them with the liquid-impermeable,vapor-permeable material 336—a single piece or a plurality of pieces.The liquid-impermeable, vapor-permeable material 336 may be coupled tothe container housing 126 using any known technique, including withoutlimitation welding (e.g., ultrasonic or RF welding), bonding, adhesives,cements, or other coupling device. As suggested by arrows 340, a liquidin the body fluids 330—typically water—evaporates and egresses throughthe windows 338. The container 304 of the illustrative embodiment ofFIGS. 5 and 6 provides structural strength from the housing 350 andprovides surface area in the windows 338 for evaporation andtransmission of the liquids from the body fluids 330.

The body fluids 330 enter the interior space 328 through a body fluidsinlet 332. In this illustrative embodiment, a reduced-pressure source322, which provides reduced pressure 323, is disposed in the interiorspace 328. For example, the reduced-pressure source 322 may be thepiezoelectric pump 354. The reduced-pressure source 322 may exhaust itspositive pressure through a vent 356. One or more electrical leads 358may provide power and control to the reduced-pressure source 322.Because the reduced-pressure source 322 is a heat-generating vacuum pumpor device, the reduced-pressure source 322 provides net thermal energy325 into the interior space 328 and thereby helps to heat the bodyfluids 330. An increase in temperature of the body fluids 330 increasesthe evaporation rate. For this reason, other approaches to increasingthe temperature of the body fluid or the liquid-impermeable,vapor-permeable member 336 may be used, such as applying the containerto the patient's skin, creating an exothermic reaction within thecontainer, using the sugar of the exudates to create power for a localelectrical heater, or other techniques.

Another illustrative embodiment involves first isolating certain liquidsfrom other components of the body fluids using an osmotic pump. Thus,for example, referring primarily to FIG. 7, another illustrativeembodiment of a container 404 for receiving and processing body fluids430, which are primarily liquids, is presented that includes an osmoticmembrane 460.

The container 404 includes a container housing 426 having an interiorspace 428 for receiving the body fluids 430. The interior space 428 hasa wound fluid portion 462 and an osmotic fluid portion 464 separated bythe osmotic membrane 460. The osmotic fluid portion 464 may have asalt-loaded wicking member 466. Water is pulled across the osmoticmembrane 460 and into the osmotic fluid portion 464.

The osmotic fluid portion 464 is in fluid communication with theliquid-impermeable, vapor-permeable material 436. Thus, water in theosmotic fluid portion 464 encounters a liquid-impermeable,vapor-impermeable material 436 and evaporation and transmission occur assuggested by arrows 440. The vapor leaves through windows 438 in thecontainer housing 426. As shown, an optional protective cover 468 may bedisposed between the liquid-impermeable, vapor-impermeable material 436and the housing frame 450.

A body fluid inlet 432 may be formed on the container housing 426. Thebody fluid inlet 432 is for receiving the body fluids 430 into theinterior space 428 of the container housing 426 and in particular intothe wound fluid portion 462. A reduced-pressure inlet 434 may beincluded in the container housing 426 to allow the introduction ofreduced pressure into the interior space 428. Alternatively, areduced-pressure source may be contained within the interior space 428.

Referring now primarily to FIG. 8, another illustrative embodiment of acontainer 504 for receiving and processing body fluids 530 is presented.The container 504 includes a container housing 526 in the form of aflexible pouch 568. The flexible pouch 568 may be contained within arigid housing (not shown).

The flexible pouch 568 is substantially formed from aliquid-impermeable, vapor-permeable material. The container housing 526has an interior space 528 for receiving the body fluids 530. Anattachment plate 570 may be attached to the container housing 526. Abody fluid inlet 532 and a reduced-pressure inlet 534 may be formed onthe attachment plate 570. If a rigid housing is used to contain theflexible pouch 568, the body fluid inlet 532 and reduced-pressure inlet534 would be coordinated with openings on the rigid housing. A foamspacer, internal polymer frame, or other spacer member (not shown) maybe coupled to the body fluid inlet 532 and reduced-pressure inlet 534(or otherwise associated with the interior space 528) to avoid a vacuumlock as the flexible pouch 568 collapses under the influence of reducedpressure.

Referring now primarily to FIG. 9, an illustrative embodiment of a wounddressing 672 for treating a tissue site 606, such as a wound 608, on apatient is presented. The wound 608 may extend through the patient'sepidermis 610. The wound dressing 672 may include a treatment manifold603 that is placed proximate to the tissue site 606. An absorbent layer674 is placed into fluid communication with the tissue site 606 toreceive body fluids therefrom. The absorbent layer 674 has a first side676 and a second, patient-facing side 678.

The wound dressing 672 may also include a first wicking layer 680 thatmay be disposed proximate to the second, patient-facing side 678 of theabsorbent layer 674. The wound dressing 672 may also have a secondwicking layer 682 that is disposed proximate to the first side 676 ofthe absorbent layer 674 and to a liquid-impermeable, vapor-permeablelayer 636. The liquid-impermeable, vapor-permeable layer 636 covers theabsorbent layer 674 and the tissue site 606 and functions as a coveringor drape. The liquid-impermeable, vapor-permeable layer 636 may be heldto the patient's epidermis 610 by an attachment device 614. Fewer layersmay be included or more layers may be added and the order of the layersmay be changed. A micropump (not shown) may be included below theliquid-impermeable, vapor-permeable layer 636 to provide reducedpressure.

Similar to other embodiments presented herein, the liquid-impermeable,vapor-permeable layer 636 is operable to allow liquids in the bodyfluids to evaporate and exit the liquid-impermeable, vapor-permeablelayer 636 as suggested by arrows 640. In this way, the absorbent layer674 is able to receive more body fluids over an elapsed time period thanthe absorbent layer 674 could retain otherwise.

In any of the embodiments herein, a flocculation agent could be added tothe interior space of the container. Thus, for example, according toanother illustrative embodiment, a body fluid in the form of a liquidfrom a tissue site is delivered through a reduced-pressure deliveryconduit, e.g., the first reduced-pressure conduit 120 in FIG. 1, to acontainer, e.g., the container 104 in FIG. 1. In the container,evaporation is promoted as presented in the various embodiments herein,but in addition the body fluid is flocculated.

Flocculation is the process that causes fine particulates to clumptogether into floc. The floc often floats to the top of the liquid,settles to the bottom of the liquid, or is filtered from the liquid. Theremaining liquid, or clarified liquid, is more pure. The clarifiedliquid may then be exposed to ion exchange materials (e.g., polymerswith strong cations and anions) to remove the salts and produce aresultant clarified liquid.

In carrying out the flocculation process, the container may contain aseparate portion on an interior of the container or elsewhere thatcontains a flocculation agent. The flocculation agent is introduced intoa portion of the container holding the body fluid in order to causeflocculation. Alternatively, the flocculation agent may be supported ona filter or non-woven material. Any suitable flocculation agent may beused including the following: polyelectrolytes, aluminum sulphate,aluminum, iron, calcium or magnesium.

The resulting clarified fluid is exposed to a liquid-impermeable,vapor-permeable material, e.g., the liquid-impermeable, vapor-permeablematerial 136 in FIG. 1, and at least of the portion of the remainingliquid evaporates and egresses the liquid-impermeable, vapor-permeablematerial. Adding flocculation to a system, such as the system 100 ofFIG. 1, may be an advantageous way of reducing fouling or potentialfouling of the liquid-impermeable, vapor-permeable material. Inaddition, the clarified fluid may evaporate more effectively and egressthe liquid-impermeable, vapor-permeable material.

Referring now primarily to FIG. 10, an illustrative embodiment of acontainer 704 for receiving and processing body fluids (primarilyliquids) from a patient is presented. The container 704 is operable toprocess more liquids over time than the container 704 can physicallyretain at one time. The container 704 is analogous to previouslypresented containers, but a forced-air device 755 has been added toincrease the rate of water vapor transport.

The container 704 includes a container housing 726 having an interiorspace 728 for receiving the body fluids 730. The container housing 726has a fluid inlet, or a body fluid inlet 732, for receiving the bodyfluids 730 from a conduit 720. The container housing 726 has a reducedpressure inlet 734 for receiving reduced pressure from a conduit 724from a reduced-pressure source (not shown). At least a portion of thecontainer housing 726 comprises a liquid-impermeable, vapor-permeablematerial 736. The liquid-impermeable, vapor-permeable material 736 mayform the whole container 104 or may form only a portion, e.g., a wall orwindow 138.

In this illustrative embodiment, evaporation and egress (see arrows 740)through the liquid-impermeable, vapor-permeable material 736 may beenhanced by forcing air 757 across an exterior of theliquid-impermeable, vapor-permeable material 736 with the forced-airdevice 755. The forced-air device 755 may be a fan that directs airacross the liquid-impermeable, vapor-permeable material 736 or fan withbaffles and ducts. The forced-air device 755 may be a fan-less devicesuch as an electrostatic device for moving air or a piezoelectric pumpwith baffles that move air. The forced-air device 755 may also be aplurality of ducts or baffles and an intentional leak in the container704 that allows reduced pressure to pull air through the ducts acrossthe liquid-impermeable, vapor-permeable material 736 before entering theinterior space 728. The movement of air across the liquid-impermeable,vapor-permeable material 736 increases the rate of water vaportransport. Without being limited by theory, the moisture gradient acrossthe liquid-impermeable, vapor-permeable material 736 may pull water fromthe wound fluid 730.

Referring now primarily to FIG. 11, an illustrative embodiment of acontainer 804 for receiving and processing body fluids (primarilyliquids) from a patient is presented. The container 804 is operable toprocess more liquids over time than the container 804 can physicallyretain at one time. The container 804 is analogous in most respects tothe previously presented containers and particularly to container 704 ofFIG. 10.

The container 804 has a container housing 826 forming an interior space828. The interior space 828 receives body fluids 830 (primarily liquids)through a delivery conduit 820 that is fluidly coupled to body fluidinlet 832. Reduced pressure may be delivered from a reduced-pressuresource through a delivery conduit 824 to a reduced-pressure inlet 834.

One or more windows 838 are formed on the container housing 826. The oneor more windows 838 may be formed by forming one or more windowapertures 835 and covering (on the interior, exterior, or a sill) thewindow aperture(s) 835 with a liquid-impermeable, vapor-permeablematerial 836. The liquid-impermeable, vapor-permeable material 836 maybe coupled to the container housing 826 using any known technique,including without limitation welding (e.g., ultrasonic or RF welding),bonding, adhesives, cements, or other coupling device.

A forced-air device 855 is positioned to provide forced air along theliquid-impermeable, vapor-permeable material 836 to increase the rate ofwater vapor transport. In this illustrative embodiment, the forced-airdevice 855 is a fan 859. The forced-air device 855 may be powered by abattery or an external connection 861. A plurality of baffles walls 863may be formed as part of or coupled to the container housing 826. Theforced-air device 855 may be coupled to a baffle wall of the pluralityof baffle walls 863. The baffle walls 863 may have a plurality of ventopenings 865 for directing air flow. The forced-air device 855 causesair to impact or move across the liquid-impermeable, vapor-permeablematerial 836.

As with other embodiments herein, vaporization of the body fluids 830may be enhanced by an interior-energy device that adds energy into theinterior space 828. The interior-energy device may be a heating elementor device for adding thermal energy, an agitator for moving the bodyfluids 830 against the window(s) 838, or a bubbler 867 to create bubbles869 in the body fluids 830. The bubbler 867 may include a small poresize filter to prevent expelling pathogenic material. The bubbler 867may have a water collection device associated with the bubbler 869 tocontain and water or liquids that may egress the bubbler 867 as itoperates. The water collection device may be a container under thebubbler 867.

In operation according to one illustrative embodiment, the container 804is fluidly coupled by delivery conduit 820 to a source of body fluids.The container 804 is also coupled by conduit 824 to a reduced-pressuresource. (In an alternative embodiment, the reduced-pressure source maybe within the container 804). The reduced-pressure source is activatedand body fluids 830 are delivered into the interior space 828. Theforced-air device 855, e.g., fan 859, is activated and air 857 is forcedto impact or move across the liquid-impermeable, vapor-permeablematerial 836 on window 838. The vapor egresses through theliquid-impermeable, vapor-permeable material 836 (see arrows 840) at anenhanced rate.

Other features may be included as an aspect of the containers 104, 204,304, 404, 50.4, 604, 704, and 804 to enhance evaporation. For example,referring now to FIG. 12, a liquid-impermeable, vapor-permeable material936 may be used that has corrugations 971. The liquid-impermeable,vapor-permeable material 936 may be used any of the embodiments hereinas the liquid-impermeable, vapor-permeable material 136, 236, 336, 436,536, 636, 736, 836, 1236, or 1336. As air 957 is forced across theliquid-impermeable, vapor-permeable material 936 more surface area mayinteract with the air. In addition or alternatively, a texturedliquid-impermeable, vapor-permeable material 1036 may be used as shownin FIG. 13. As shown in FIG. 14, the liquid-impermeable, vapor-permeablematerial 1136 may include flocking 1173 or fine fibers that provideadditional area on an exterior portion of the liquid-impermeable,vapor-permeable material 1136. In addition to the flock 1173 or finefibers, other porous wicks may be employed such as hydrophylic,open-celled foam (e.g., polyurethane, polyvinyl alcohol, cellulose); orsintered polymers (e.g., polyolefin, polyamide, polyester, acrylic)surface treated to be hydrophylic.

Referring now primarily to FIG. 15, an illustrative embodiment of acontainer 1204 for receiving and processing body fluids (primarilyliquids) from a patient is presented. The container 1204 is operable toprocess more liquids over time than the container 1204 can physicallyretain at one time. The container 1204 is analogous to previouslypresented containers, but the interior-energy device is different. Theinterior-energy device is a conduit 1269 and valve 1271 that have beenadded to increase energy within an interior space 1228. Theinterior-energy device is a conduit 1269 moves the liquids within theinterior space 1228.

The container 1204 includes a container housing 1226 having the interiorspace 1228 for receiving the body fluids 1230. The container housing1226 has a fluid inlet 1232 for receiving the body fluids 1230 from aconduit 1220. The container housing 1226 has a reduced pressure inlet1234 for receiving reduced pressure from a conduit 1224 from areduced-pressure source (not shown). At least a portion of the containerhousing 1226 comprises a liquid-impermeable, vapor-permeable material1236. The liquid-impermeable, vapor-permeable material 1236 may form thewhole container 1204 or may form only a portion, e.g., a wall or window1238. The liquid-impermeable, vapor-permeable material 1236 is showncoupled on an exterior of the container 1204, but could also be on theinterior or flush with the container 1204.

The valve 1271 and conduit 1269 provide energy in the form of bubblesinto the interior space 1228. The valve 1271 provides control of the airentering the sealed space 1228. The valve may restrict or close offfluid flow in the conduit 1269 and thereby control the flow therein. Thevalve 1271 may be manually operated or include solenoid or other controldevice that is coupled to a controller. The flow of air through conduit1269 may be controlled and may be constant or intermittent.

Referring now primarily to FIG. 16, another illustrative embodiment of acontainer 1204 for receiving and processing body fluids (primarilyliquids) from a patient is presented. The container is analogous to thecontainer of FIG. 15 and the same reference numerals are used. The maindifference between the embodiments of FIGS. 15 and 16 is that theconduit 1269 and valve 1271 have been replaced with an interior-energydevice in the form of a longitudinal bubbler 1267. The longitudinalbubbler 1267 is fluidly coupled to the valve 1273.

The longitudinal bubbler 1267 delivers additional energy in the form ofbubbles into the interior space 1228. The longitudinal bubbler 1267 maybe any device that distributes bubbles within the interior space 1228.For example, the longitudinal bubbler 1267 may be a porous,gas-permeable, water-impermeable, hydrophobic member, such as a sinteredpolymer membrane, PTFE, or other suitable material. As with valve 1271,valve 1273 may deliver air continuously or intermittently.

Referring now primarily to FIG. 17, an illustrative embodiment of acontainer 1304 for receiving and processing body fluids (primarilyliquids) from a patient is presented. The container 1304 is operable toprocess more liquids over time than the container 1304 can physicallyretain at one time. The container 1304 is analogous in many respects tothe previously-presented containers.

The container 1304 has a container housing 1326 forming an interiorspace 1328. The interior space 1328 receives body fluids 1330 (primarilyliquids) through a delivery conduit 1320 that is fluidly coupled to abody fluid inlet 1332. Reduced pressure may be delivered from areduced-pressure source through a delivery conduit 1324 to areduced-pressure inlet 1334.

The container housing 1326 has an inner wall 1373 and an outer wall1375, or shell. The space between the inner wall 1373 and outer wall1375 forms a passageway 1377. One or more spaced support members 1379may be used to hold the inner wall 1373 and outer wall 1375 in relativeposition to one another. Alternatively or in addition to spaced supportmembers 1379, the space between the inner wall 1373 and the outer wall1375, i.e., the passageway 1377, may be filled with a porous, continuousor substantially continuous support.

One or more windows 1338 are formed on the container housing 1326. Theone or more windows 1338 may be formed by forming one or more windowapertures 1335 and covering the window aperture(s) 1335 with aliquid-impermeable, vapor-permeable material 1336. Theliquid-impermeable, vapor-permeable material 1336 may be coupled to thecontainer housing 826 using any known technique, including withoutlimitation welding (e.g., ultrasonic or RF welding), bonding, adhesives,cements, or other coupling device. As with the other embodiments, theliquid-impermeable, vapor-permeable material 1336 may be attached withinthe window aperture(s) 1335 as shown or may be on an interior orexterior of the container housing 1326.

A passageway inlet 1381 is formed in the container housing 1326 to allowfluid access to the passageway 1377. A forced-air device 1355 ispositioned to deliver forced air into the passageway inlet 1381. Theforced air 1378 moves through the passageway 1377 and across theliquid-impermeable, vapor-permeable material 1336. A passageway outlet1380 is formed in the container housing 1326 to allow the forced air1378 and vapor to exit the passageway 1377. In another embodiment, theforced-air device 1355 may be positioned within the passageway 1377.

A wicking layer 1382 may be coupled to an interior of the inner wall1373. The wicking layer 1382 spreads the liquids in the interior space1328 around and causes more liquid contact with the liquid-impermeable,vapor-permeable material 1336. The wicking layer 1382 may cover only theliquid-impermeable, vapor-permeable material 1336 or may cover theentire interior of the inner wall 1373. A filter layer 1383 may becoupled to an interior side of the wicking layer 1382. The filter layer1383 may be used to reduce the amount of fluid-borne particulatereaching and possibly fouling the wicking layer 1382.

With respect generally to forced-air devices 755, 855, 1355, which mayadded to any of the embodiments herein, the forced air flow may beintermittent (e.g., pulsed) or continuous. Moreover, the air flow may bereversed to flow in the opposite direction. A humidity or moisturesensor may be placed downstream of the liquid-impermeable,vapor-permeable material involved. The humidity or moisture sensor maybe coupled to a controller or otherwise configured to switch off theforced-air device 755, 855, 1355 when moisture levels detected are belowa minimum threshold over a time interval. In another embodiment, ahumidity or moisture sensor may be placed inside the interior space ofthe container and the forced-air device only activated when moisture isdetected in the interior space.

Although the present invention and its advantages have been disclosed inthe context of certain illustrative, non-limiting embodiments, it shouldbe understood that various changes, substitutions, permutations, andalterations can be made without departing from the scope of theinvention as defined by the appended claims. As an non-limiting example,it should be understood that the osmotic membrane 460 of FIG. 7 may beincluded in the interior space 828 of the container 804 of FIG. 11. Asanother non-limiting example, the waffle pockets 246 of FIG. 4 may beadded to the other embodiments herein. As another non-limiting example,the protective cover 468 of FIG. 7 could be added to other embodimentsherein. As yet another non-limiting example, the bubbler 867 orforced-air device 855 of FIG. 11 could be added to any of theembodiments herein.

It will be understood that the benefits and advantages described abovemay relate to one embodiment or may relate to several embodiments. Itwill further be understood that reference to “an” item refers to one ormore of those items.

The steps of the methods described herein may be carried out in anysuitable order, or simultaneously where appropriate.

Where appropriate, aspects of any of the embodiments described above maybe combined with aspects of any of the other embodiments described toform further embodiments having comparable or different properties andaddressing the same or different problems.

It will be understood that the above description of preferredembodiments is given by way of example only and that variousmodifications may be made by those skilled in the art. The abovespecification, examples and data provide a complete description of thestructure and use of exemplary embodiments of the invention. Althoughvarious embodiments of the invention have been described above with acertain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thescope of the claims.

We claim:
 1. A system for treating a tissue site with reduced pressure,the system comprising: a manifold configured to be placed proximate tothe tissue site; a reduced-pressure source; and a container forreceiving body fluids from the tissue site, the container comprising: aliquid-impermeable, vapor-permeable layer defining a portion of a sealedspace, the liquid-impermeable, vapor-permeable layer comprising: a firstsurface treated to enhance hydrophilicity; and a second surface oppositethe first surface, the second surface configured to be exposed to anambient environment surrounding the container; a fluid inlet fluidlycoupled to the sealed space and configured to be fluidly coupled to themanifold; and a fluid outlet fluidly coupled to the sealed space andconfigured to be fluidly coupled to the reduced-pressure source.
 2. Thesystem of claim 1, wherein the container further comprises a wickinglayer disposed in the sealed space and coupled to theliquid-impermeable, vapor-permeable layer.
 3. The system of claim 1,further comprising an attachment device configured to couple thecontainer to the tissue site.
 4. The system of claim 1, wherein theliquid-impermeable, vapor-permeable layer is corrugated.
 5. The systemof claim 1, wherein the liquid-impermeable, vapor-permeable layer isflocked.
 6. The system of claim 1, wherein the liquid-impermeable,vapor-permeable layer is textured.
 7. The system of claim 1, wherein thecontainer further comprises an absorbent layer within the sealed space,the absorbent layer having a first side and a second side, the absorbentlayer in fluid communication with the tissue site and operable toreceive body fluids from the tissue site.
 8. The system of claim 7,wherein the liquid-impermeable, vapor-permeable layer is operable toallow liquid from the body fluids from the absorbent layer to evaporateand exit the liquid-impermeable, vapor-permeable layer.
 9. The system ofclaim 7, wherein the container further comprises a first wicking layerproximate to the second side of the absorbent layer.
 10. The system ofclaim 9, wherein the container further comprises a second wicking layerproximate to the first side of the absorbent layer.
 11. A container forstoring fluids from a tissue site treated with reduced pressure, thecontainer comprising: a liquid-impermeable, vapor-permeable materialdefining a portion of a sealed space of the container, a fluid inletfluidly coupled to the sealed space; and a fluid outlet fluidly coupledto the sealed space; wherein the liquid-impermeable, vapor-permeablematerial is adapted to contact and retain fluids received in the sealedspace, the liquid-impermeable, vapor-permeable material having a surfacetreated to enhance hydrophilicity.
 12. The container of claim 11,further comprising a wicking layer disposed in the sealed space andfluidly coupled to the liquid-impermeable, vapor-permeable material. 13.The container of claim 11, further comprising an attachment deviceconfigured to couple the liquid-impermeable, vapor-permeable material tothe tissue site.
 14. The container of claim 11, wherein theliquid-impermeable, vapor-permeable material is corrugated.
 15. Thecontainer of claim 11, wherein the liquid-impermeable, vapor-permeablematerial is flocked.
 16. The container of claim 11, wherein theliquid-impermeable, vapor-permeable material is textured.
 17. Thecontainer of claim 11, further comprising a reduced-pressure sourcecoupled to the liquid-impermeable, vapor-permeable material, thereduced-pressure source configured to provide reduced pressure to thetissue site.
 18. The container of claim 11, further comprising anabsorbent layer within the sealed space, the absorbent layer having afirst side and a second side, the absorbent layer in fluid communicationwith the tissue site through the fluid inlet and operable to receivebody fluids from the tissue site.
 19. The container of claim 18, whereinthe liquid-impermeable, vapor-permeable material is operable to allowliquid from the body fluids from the absorbent layer to evaporate andexit the liquid-impermeable, vapor-permeable material.
 20. The containerof claim 18, further comprising a first wicking layer proximate to thesecond side of the absorbent layer.
 21. The container of claim 20,further comprising a second wicking layer proximate to the first side ofthe absorbent layer.
 22. A system for treating a tissue site withreduced pressure, the system comprising: a container for storing fluidsfrom the tissue site, the container comprising: a liquid-impermeable,vapor-permeable layer defining a portion of a sealed space of thecontainer, a fluid inlet fluidly coupled to the sealed space; and afluid outlet fluidly coupled to the sealed space; wherein theliquid-impermeable, vapor-permeable layer is adapted to contact andretain fluids received in the sealed space, the liquid-impermeable,vapor-permeable layer having a surface treated to enhancehydrophilicity; and a reduced-pressure source fluidly coupled to thefluid outlet.
 23. The system of claim 22, wherein the container furthercomprises a wicking layer disposed in the sealed space and fluidlycoupled to the liquid-impermeable, vapor-permeable layer.
 24. The systemof claim 22, further comprising an attachment device configured tocouple the container to the tissue site.
 25. The system of claim 22,wherein the liquid-impermeable, vapor-permeable layer is corrugated. 26.The system of claim 22, wherein the liquid-impermeable, vapor-permeablelayer is flocked.
 27. The system of claim 22, wherein theliquid-impermeable, vapor-permeable layer is textured.
 28. The system ofclaim 22, wherein further comprising a manifold configured to beproximate the tissue site.
 29. The system of claim 22, wherein thecontainer further comprises an absorbent layer within the sealed space,the absorbent layer having a first side and a second side, the absorbentlayer in fluid communication with the tissue site and operable toreceive body fluids from the tissue site.
 30. The system of claim 29,wherein the liquid-impermeable, vapor-permeable layer is operable toallow liquid from the body fluids from the absorbent layer to evaporateand exit the liquid-impermeable, vapor-permeable layer.
 31. The systemof claim 29, wherein the container further comprises a first wickinglayer proximate to the second side of the absorbent layer.
 32. Thesystem of claim 31, wherein the container further comprises a secondwicking layer proximate to the first side of the absorbent layer.